Spark plug



0. C. ROHDE April 5, 1932.

SPARK PLUG Filed Jan. 29 1932 Patented. Apr. 5,-

} UNITED STATES PATENT OFF-ICE TOLEDO, OHIO, ABSIGNOR T CHAMPION SPARKPLUG COMPANY, OI TOLEDO, OHIO, A CORPORATION OI OHIO v arm rmroApplication fled January, 1932. Serial in. 589,877.

This invention relates to a spark pl u" and more particularly to theconstruction 0 porcelain type core for a plug. The invention has tor itspur ose to provide a spark plug with a core which will'have the variousportions thereof maintained at proper working ill lit

temperature under the conditions for which the plug is intended.

in high compression and high duty internal combustion motors thetemperatures to which the inwardly projecting end of the spark plug coreis subjected are relatively high and there is danger of portions of thecore becoming so highly heated that preignition results. In order toprevent overheating oi the inner end of the core the heat must becarried ofi fairly rapidly. Any sharp line ct division between thehotter and cooler portions of the core is apt to result in breaking orsplitting of the core. For this reason a proper heat gradient betweenthe several portions of the core must be main-s tained. 7

When portions of the core are maintained below a certain temperature,carbon is deposited thereon. As the core becomes hotter, such carbondeposits are burned ofi until a certain point is passed, after whichcarbon is again condensed upon the core in a form lmown as incrusted,carbon. In modern ractice the inner end of the core is usually mated tosuch an extent that there is incrusted carbon. In order to properly coolthe core and prevent preignition, the portion of the core adjacent itsseat in the shell is usually cool enough to have thereon a deposit ofcarbon. If the incrusted carbon reaches close to the dc osited carbon,the insulation of the core 1s reduced to such an extent as to destroythe usefulness of the plug. It is, therefore, necessary to rovide amaterial length of core which will e normally free from either incrustedor deposited carbon, as defined above.

Thepurpose of the present invention is to provide a core and shellproperly related so as toguard against preignition'and to provide anample length of core which will be normally free from either incrustedor deposited carbon and eliminate any region Figure 1 is a longitudinalsection through so a plug embodying one form of the invention and 1nwhlch the inner end of the core extends beyond the surrounding shell;and

Flgure 2 is a view similar to Fig. 1, but showing a beyond the inner endof the core.

-The plug disclosed in Fig. 1 comprises a shell 10 of common type havingan inner screw threaded end 11 ada ted to be screwed into,

the combustion cham er of an internal com- I0 bustion motor. The shellis provided with a slight? restricted end portion 12 andhas a shoul er13 supporting a gasket 14 on whlch there rests a core 15. The core isprovided with a downwardly facing seating 75 surface 16 u on itsshoulder 17, which seatmg surface 1s adapted to rest upon gasket 14. Theshoulder has an upwardly facing seating surface 18 against which agasket 19 is pressed by a sleeve 20 screwed into the 80 upper portion ofshell 10. An electiode 21 asses through the core and extends at itslnner end 22 into sparking relation with an eaeciiirode 23 attached tothe inner end of the s e The construction as thus far described iscommon, and is merely indicated for the purpose of showing the settingof the improvement constituting the present invention.

The lower end of the core as shown in Fig. 9c

1 extends at 25 beyond the inner end of the shell, and from its lowerend flares outwardly 1n a substantially conical shape, as indicated at26, until it reaches a bulge 27, 'which is within the restrictedIportion 12 of the lower 95 end of the shell. mmediately above the bulge27 there is an inwardly tapering portion 28 which is shorter thanportion 26 and has a somewhat steeper gradient. Above portion 28 thereis a substantially cylindrical W1 lug a vantages of which will plughaving its shell extending cs pggtion 29 extending for a materialdistance. ferably this cylindrical-portion is longer than portion 28 butnot of greater length than portion 26. Above portion 29 the core flares5 outwardly at 30 upward to the seat 16. In the form shown there is aslightl stee er gradient 31 immediately above t e cy drical portion thanthere-is'just below the seat. The construction shown in Fig. 2 issimilar to that shown in Fi 1 and hke reference numerals are applietolike parts, with a prime added for Fig. 2. The chief distinctionbetween the two figures is that in Fig. 2 portion -11' is extendeddownward beyond 15 the inner end of the core, or the core is shortenedso that it does not extend as far as the shell. Under thesecircumstances it is preferable to have shoulder 27 above restrictedportion 12 instead of within such restricted portion, as is preferablewhen the tip of the core extends below the shell. In the constructionshown in Fig. 2 cylindrical portion 29' is shortened, but it is stilllonger, than tapered portion28.

Attention is called to the fact that the diameter of the electrode 21 issubstantially uniform and that there is no enlargement of this electrodewhere it extends below the core. Any enlargement of the extending innerend of the electrode, particularly if such enlargfment is in directcontact with the core, is hig ly objectionable because the electrode isnormally of higher heat conductivity than the core and as a consequencesuch enlar ement of the inner end of the electrode resu ts intransmission of excessive heat to the portion of the. core in contacttherewith.

The outward flaring portion 26 provides increasin space above t e tipfor the carr ing off 0 heat and in this way reduces t e extremetemperature of the end ofthe tip and thereby decreases the danger ofpreignition. It has been found. preferable to maintain. this flare alonsubstantially conical lines in order to obtaln the desirable heatgradient. V

Bulge 27 between flare portions 26 and 28 is somewhat rounded in orderto prevent any sha edge, since a sharp projecting edge, articularly nearthe inner end of the core, is likely to become overheated and causepreignition.

The inwardly tapered portion 28 and the substantially cylindricalportion 29 provide a fairly long) surface which is normally hot enoughto urn ofl' deposited carbon and not hot enough to be covered withincrusted carbon, and, therefore, maintains an effective insulatingsurface. This reduced cylindrical o0 portion decreases the crosssectional area of the core through which heat may be carried off fromthe tip to the seating shoulder and thereby prevents the cooling of thisportion of the core to such an extent that carbon is deposited thereon.The changes in direction .is lik of'the surface of the core are allgradual so as to prevent either an external angle, which e y to becomeoverheated and cause preignition, or a reentrance angle sufiiciently sarp to make a distinct line where the temperature gradient is so steepas to cause split ting of the core.

As previously indicated, it has been found preferable, where the core isextended below the shell, to locate the bulge 27 within restrictedportion 26 of the core. Less satisfactory results are obtained fromhavin this bulge either below or above the restriction under suchcircumstances; but where the inner end of the tip does not extend beyondthe shell, it is found preferable to have the bulge above the restrictedportion of the shell, as indicated in Fig. 2.

While the particular shape of the core indicated in the figures is thebest embodiment of the invention at'present known for the majority ofmotors now in use, it will be understood that some changes may be made,particularly to suit varying conditions, within the scope of theappended claims, it being f particularly borne in mind that increasingthe diameter of the' core above a given point tends to decrease thetemperature at said point, while decreasing the cross section of thecore above a given point tends to increase the temperature at saidpoint. Itwill be further understood that any conducting materialcontacting the outer surface of the core between its seat and tip notonly interrupts the insulating surface upon which dependence is placedto insulate the central electrode from the shell, but also isobjectionable because of its greater heat conductivity and consequentdisturbance of proper heat distribution in the core. While reference hasderstood that the invention applies to other materials having similarcharacteristics as heat conductivity, etc.

What I claim is: g I

.1. A spark plug core-having a downwardly facing seating surface, thecore between said seating surface and its lower end presenting onecontinuous insulating surface with only curvin changes in direction andconsisting of an mtermediate substantially cylindrical restrictedportion, a single enlargement between said portion and said lower end,and a portion enlarging from said restricted portion to said seatinsurface, the heat transfer being v from said enlarged end portionthrough said restricted ortion and then through said enlarged seatingportion whereby'a carbon free zone is provided at said restrictedportion.

2. A. spark plug core having a shoulder with a downward facing seatingsurface and an electrode embedded in and projecting from the lower endof the core, the cross section of the lower part of the embedded por-.

been'made to a porcelain core, it will be untion of the electrode beingas large as the cross section at any point of the projecting end of theelectrode, the core presenting one continuous insulating surface withonly curving changes of direction between said seating surface and itslower end, and the core having a single enlargement adjacent its lowerend and a single restricted portion be tween said enlargement and saidseating surface, whereby the heat transfer is from said enlarged endportion through said restricted portion and a carbon free zone isprovided at said restricted portion.

3. A spark plug core having a downwardly facing seating surface and anelectrode extending through the core and projecting from its lower end,said electrode being of substantially uniform cross section from itslower end to at least as high as said seating surface, the core betweensaid seating surface and its lower end presenting one continuousinsulating surface with only curving changes in direction and consistingof an intermediate substantially cylindrical portion, a singleenlargement between said portion and said lower end, and a portionenlarging from said cylindrical portion to said seating surface, theheat transfer from said enlarged end portion through said cylindricalportion and then through said enlarged seating portion whereby a carbonfree zone is provided at said cylindrical portion.

4:. A spark plug core having a downwardly seating shoulder and a tip,said core flaring from its tip to a bulge, tapering from the bulge to asubstantially cylindrical portion, and flaring from the upperend of saidcylindrical portion to its seat, the first said flare being at least aslong as said cylindrical por-' tion and said taper being shorter thansaid cylindrical portion, whereby the heat transfer is from saidenlarged end portion through said cylindrical portion and a carbon freezone is provided at said cylindrical portion.

5. A core in accordance with claim 4 and in which the first said flareis substantially conical.

6. A spark plug comprising a shell havin a seat for a core and arestricted inner en and a core with a shoulder having a downwardlyfacing surface cooperating with said seat, the core projecting inwardfrom said seat farther than the shell and flaring outward from its tipsubstantially conically to a bulge within but out of contact with therestricted portion of said shell, tapering from the bulge to asubstantially cylindrical portion and flaring from the upper end of thecylindrical portion to said downwardly facing surface, the distance fromthe bulge to the cylindrical portion being substantially less than thatfrom the cylindrical portion to the seat.

7. spark plug. comprising ashell having a seat for a core and arestricted inner end, and a core with a shoulder having a downwardlyfacing surface cooperating with said seat, the core projecting inwardfrom said seat to a tip within said restricted portion of the shell, thecore flaring upward from the tip to a bulge located above the restrictedportion of the shell, tapering from the bulge to a substantiallycylindrical portion and flaring from the upper end of the cylindricalportion to said downwardly facing surface, the heat transfer being fromsaid enlarged end portion through said cylindrical portion and thenthrough said enlarged seating portion whereby a carbon free zone isprovided at said cylindrical portion.

8. A spark plug comprising a core having a seating surface andprojecting inward from said surface to a tip, and an electrode embeddedin the core and projecting from said tip, the cross section of the lowerend of the embedded portion and the projecting portion of the electrodebeing substantially uniform, the core flaring outward from its tip tocarry off the heat from the tip and minimize preignition, having arestricted portion of substantial length above said flaring portion toretain sufficient heat to eliminate deposited carbon, flaring from theupper end of said restricted portion to said seating surface, presentinan insulating surface from seat to tip to avoid disturbance of heatdistribution, and changing in contour gradually to avoid excessive heatgradients.

In testimony whereof I have hereunto signed my name to thisspecification.

OTTO O. ROHDE.

